Buggy code:
public abstract class AbstractExpressionVisitor extends AbstractVisitor { @ Override public final Object visit ( final ISyntaxElement ele ) { Object result = null ; <START_BUG> if ( ( result == null ) && ( ele instanceof BooleanOperation ) ) { <END_BUG> result = visitBooleanOperation ( ( ( BooleanOperation ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof Cast ) ) { result = visitCast ( ( ( Cast ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof ConstructorCallExpression ) ) { result = visitConstructorCallExpression ( ( ( ConstructorCallExpression ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof GlobalVarExpression ) ) { result = visitGlobalVarExpression ( ( ( GlobalVarExpression ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof ChainExpression ) ) { result = visitChainExpression ( ( ( ChainExpression ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof CollectionExpression ) ) { result = visitCollectionExpression ( ( ( CollectionExpression ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof OperationCall ) ) { result = visitOperationCall ( ( ( OperationCall ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof TypeSelectExpression ) ) { result = visitTypeSelectExpression ( ( ( TypeSelectExpression ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof FeatureCall ) ) { result = visitFeatureCall ( ( ( FeatureCall ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof IfExpression ) ) { result = visitIfExpression ( ( ( IfExpression ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof LetExpression ) ) { result = visitLetExpression ( ( ( LetExpression ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof SwitchExpression ) ) { result = visitSwitchExpression ( ( ( SwitchExpression ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof ListLiteral ) ) { result = visitListLiteral ( ( ( ListLiteral ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof BooleanLiteral ) ) { result = visitBooleanLiteral ( ( ( BooleanLiteral ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof IntegerLiteral ) ) { result = visitIntegerLiteral ( ( ( IntegerLiteral ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof NullLiteral ) ) { result = visitNullLiteral ( ( ( NullLiteral ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof RealLiteral ) ) { result = visitRealLiteral ( ( ( RealLiteral ) ( ele ) ) ) ; } if ( ( result == null ) && ( ele instanceof StringLiteral ) ) { result = visitStringLiteral ( ( ( StringLiteral ) ( ele ) ) ) ; } return result ; } protected Object visitBooleanOperation ( BooleanOperation node ) { } protected Object visitCast ( Cast node ) { } protected Object visitConstructorCallExpression ( ConstructorCallExpression node ) { } protected Object visitGlobalVarExpression ( GlobalVarExpression node ) { } protected Object visitChainExpression ( ChainExpression ce ) { } protected Object visitFeatureCall ( FeatureCall fc ) { } protected Object visitCollectionExpression ( CollectionExpression node ) { } protected Object visitOperationCall ( OperationCall oc ) { } protected Object visitTypeSelectExpression ( TypeSelectExpression node ) { } protected Object visitIfExpression ( IfExpression node ) { } protected Object visitLetExpression ( LetExpression node ) { } protected Object visitSwitchExpression ( SwitchExpression node ) { } protected Object visitListLiteral ( ListLiteral node ) { } protected Object visitBooleanLiteral ( BooleanLiteral node ) { } protected Object visitIntegerLiteral ( IntegerLiteral node ) { } protected Object visitNullLiteral ( NullLiteral node ) { } protected Object visitRealLiteral ( RealLiteral node ) { } protected Object visitStringLiteral ( StringLiteral node ) { } }

Fix:
if ( ele instanceof BooleanOperation ) {